The methods of the embodiments described herein relate to high-temperature lubricants comprising elongated carbon nanoparticles for use in downhole cutting tools and methods for their manufacture.
As used herein, the term “downhole cutting tool” in all of its forms refers to any variety of downhole tools that can be operated to form a well bore in the ground by drilling, such as to reach a desired subterranean formation. Examples of downhole cutting tools include, but are not limited to, a roller cone bit, a polycrystalline diamond compact bit, a drag bit, an impregnated bit, a reamer with cutting elements, and the like. A downhole cutting tool includes cutting elements that help the cutting tool penetrate the ground by liberating earthen materials, such as by shearing or crushing adjacent formation materials contacted by the cutting elements. Associated drilling technologies, such as the circulation of drilling fluids down through a drill string and up through an annulus formed between the drill string and the well bore, are used to continually remove formation materials and other debris from the well bore. The rate of penetration of a downhole cutting tool is one measure of drilling efficiency. As used herein, the term “rate of penetration” (“ROP”) refers to the rate at which a hole can be drilled in the ground. ROP may be expressed in terms of depth over time that a well bore is formed when drilling, such as in feet per hour.
A downhole cutting tool has to be replaced periodically due to wear on certain components, such as bearings, bearing assemblies, bearing surfaces, seals, and other supporting structures (collectively referred to herein as “supporting structures”). Replacing worn parts typically requires time-consuming steps, such as ceasing drilling operations, removing (i.e., “tripping out”) the drilling assembly from the well bore, replacing the supporting structures or the entire downhole cutting tool, and tripping the drilling assembly back down the well bore to continue drilling. The downtime associated with such replacement is costly. Because lubrication reduces friction and associated wear between moving parts, lubricants are often used to lubricate the supporting structures in downhole cutting tools. Lubrication thus extends the life of downhole cutting tools and, thus, the time between any required replacement.